自制优格（焖烧锅） Homemade Yoghurt (Thermal Cooker)

以前在大学时期上微生物学课，有一堂的实验就是要教我们利用微生物做优格。

时隔多年，我记得的，只有Lactobacillus bulgaricus这个菌种和我们做实验做到晚上的情景。

真有愧于lab demo。。呵呵。。

前几天看到超市在做促销，于是买了两公升的牛奶回家。

趁着这个机会来试一试我想做很久的《自制优格》。

只需花个10分钟的准备功夫，再把焖烧锅放一边，就可以了。

8个小时一到，迫不及待地查看成品。

当把盖子一掀开来，淡淡的优格香就飘来了！

把锅子摇一摇，牛奶变得浓稠了，上面还有一些结块，并有一层乳清。

成功了！

真的很兴奋！

把自制优格收入冰箱冷藏之后，晚上做功课做得累时来一碗当宵夜。

这次的成品闻起来和吃起来的味道跟市售的一样！

不过，texture就没市售那样浓稠得结块，这次的成品比较稀薄。

不过，整体来说，还是让人满意的。

单单吃优格，我都觉得很好吃！

或许，下次可以试一试用不同的牛奶牌子，不同的优格牌子，或许成品会不一样。

材料：
牛奶--800-1000 ml
市售优格--1罐（约140g）（确保有Lactobacillus acidophilus, Lactobacillus bulgaricus 和 Streptococcus thermophilus 的菌种）
白糖--2 tbsps（可加可不加）

做法：

1. 市售优格取出放室温约30分钟。
2. 将牛奶倒入干净的焖烧锅内锅，以中小火加热至牛奶的边缘开始出现小气泡，熄火。
3. 让牛奶降温至约40-43度C。（没有温度计，可用手指沾牛奶，温度比体温稍微高一些即可）
4. 将市售优格倒入牛奶中，用干净的汤匙搅拌均匀。
5. 把内锅盖上盖子，锁入焖烧锅外锅，让其保温。
6. 让牛奶静置8-12个小时，才可以掀开盖子看成品。
7. 如果牛奶已经变浓稠或如豆腐花状，并带有优格的清香，就代表牛奶发酵成功！
8. 将自制优格倒入事前已消毒过并晾干的瓶子里，放入冰箱冷藏。

备注：

1. 当自制优格发酵好时，优格的表面会出现一层透明的乳清。这乳清有营养，可以吃，千万不要倒掉。
2. 瓶子可以用沸水烫过，再用吹风筒吹干或放入烤箱烤片刻作消毒的作用。
3. 购买市售优格时，确保里头含有上述所说的菌种，并且不要过期，不然优格会做不成。
4. 基本上只要确保牛奶的温度不过高，并可以保持在40-43度C，那牛奶发酵的成功机率就会很高了。（因为过高的温度会将菌种杀死）
5. 如果家中没有焖烧锅，可以用较大的保温瓶做但分量自行斟酌，并用毛巾将保温瓶包起来，帮助保温。

食后感：

1. 味道（闻）：和市售优格的一样
2. 味道（吃）：和市售优格的一样
3. 浓稠度（Texture）：比牛奶浓稠但比市售优格稀薄

自我检讨：

这次的牛奶和市售优格我用了DutchLady牌，即是UHT（Ultra High Temperature）的牛奶，而且还是low fat的。或许这是造成自制优格不太能如市售般浓稠的原因吧。因为在UHT杀菌的过程，可能把有助于帮助牛奶凝结的蛋白质给毁掉了。

此外，一些人也发觉，当他们使用低脂牛奶制作优格，成品比用全脂牛奶来得稀薄。

*下次可以试试使用没有经过UHT杀菌过程的全脂牛奶来做优格，看看成品会不会比较浓稠。

Ingredients：
Milk--800-1000 ml
Store-bought Yoghurt--1 cup（Approx. 140g）（Make sure that it contains Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus ）
Sugar--2 tbsps（Optional）

Method：

1. Remove the store-bought yoghurt from fridge and put it under room temperature for approx. 30 mins.
2. Pour the milk into a clean inner pot of thermal cooker. Heat over medium low heat til it started to form small bubbles at the edge. Off the heat.
3. Let the milk cool down to approx. 40-43oC. (If there is no thermometer to measure the temperature, touch the milk with your clean finger to feel it. Ideally it should be slightly warmer than your body temperature)
4. Pour the store-bought yoghurt into the milk and stir gently with a clean spoon.
5. Cover the inner pot with its lid, lock it into the insulator to let it insulate.
6. Set the thermal cooker aside for 8-12 hours for fermentation to take place, do not open the lid before that.
7. If the milk has become thicker in texture or coagulated and possess fragrant of yoghurt, it means the milk has successfully fermented into yoghurt!
8. Pour the homemade yoghurt into a pre-sterilized bottle. Refrigerate.

Note：

1. Once fermentation has completed, there is a layer of clear liquid which is known as whey. It is nutritious, so, do not discard it.
2. The bottle can be sterilized by pouring boiling water in it and blow dry with hair dryer or heat it in an oven for a while.
3. Make sure that the store-bought yoghurt contains the above-mentioned bacteria strains and do not buy expired yoghurt, else it will cause failure in making yoghurt.
4. Basically, as long as the milk temperature is not too high and can be maintained at 40-43oC, the chances of making yoghurt successfully is high. (This is because high heat will kill the bacteria strains which are essential for fermentation to take place)
5. If there is no thermal cooker in your house, you can use a big thermos to make your own yoghurt (adjust the quantity accordingly) and wrap the thermos with a thick towel as to facilitate in insulation.

Feedback：

1. Smell：Same as store-bought yoghurt
2. Taste：Same as store-bought yoghurt
3. Texture：Thicker than milk but thinner than store-bought yoghurt

Self-reminder：

I used 'DutchLady' milk and yoghurt in this try wherein the milk is UHT (Ultra High Temperature) milk and it is a low fat milk as well. This could be the reasons that causing my homemade yoghurt does not have the thick consistency as the store-bought yoghurt. This is due to the reason that during UHT pasteurization process, some proteins which are able to help to set the milk have been denatured.

Besides, some people noticed that when they were using low fat milk to make yoghurt, the end product seems to be thin and runny.

*Maybe I should try using non-UHT full cream milk in my next attempt to see whether the homemade yoghurt has thicker consistency.